Dibasic acid esters of glycols



United States Patent 1 2,703,811 DIBASIC ACID ESTERS OF GLYCOLS Paul V. Smith, In, Westfield, N. 1., or to Esso llgeefiarch and Engineering Company, a corporation of were N6 Drawing. Application 0mm 1, 194a,

Serial No. 52,429

9 Claims. (cl. 260-485) This invention relates to a new class of compounds which have been foundto be particularly suitable for use as synthetic lubricants because of their low pour points and high viscosity indices.

In the lubricant art, considerable progress has been realized in recent years in the production of lubricants characterized by one or more specific properties and adapted for particular uses. In the main, this progress can be attributed to two developments: the first, new refining procedures, and the second, addition agents capable of imparting particular properties to available lllbllcants. Thus, viscosity index improvers and pour depressants are added to automotive lubricants to render the lubricants more adaptable to wide changes in temperature conditions, while other agents are added to improve the load-carrying properties of a lubricant which is to be employed, for example, under extreme pressure conditions.

Recently, in an effort to obtain superior lubricants endowed with specific and superior characteristics, a new field has been explored, namely the synthesis of lubricants from various materials. Esters represent one class of materials which have attracted unusual interest as synthetic lubricants. In general, they are characterized by higher viscosity indices and lower pour points than mineral oils of corresponding viscosity. The esters described in the present specification have been found to exhibit very low pour points and high viscosity indices. Lubricants possessing such properties are of special value in the lubrication of engines which are subjected to high temperatures, such as combustion turbine engines, particularly those of the prop-jet type. Mineral oil lubricants containing added viscosity index improvers, thickeners or other highly non-volatile additives are undesirable for use in such engines because of the tendency to leave a residue which accumulates and interferes with the operation of the engine. A synthetic lubricant of the type described in the present specification is especially adapted to use under such conditions, since the lubricant contains no additives and thus tends to leave no residue upon volatilization.

The new compounds of the present invention which have been found to be particularly suitable for use as lubricating oils are complex esters prepared by reacting one mol of a monohydric alcohol with one mol of a dibasic acid, thereby forming the half-ester of the dibasic acid, after which two mols of such half-ester are reacted with one mol of a glycol. The new class of compounds may bebroadly defined by the following general formula:

000m where R1 and R1 are aliphatic hydrocarbon radicals, straight chain or branched, saturated or unsaturated, each containing 0 to 30 carbon atoms, or they may be organic radicals consisting of a series of saturated aliphatic hydrocarbon radicals interlinked by atoms of oxygen or sulfur, or both oxygen and sulfur, provided there are at least 2 carbon atoms between each pair of oxygen or sulfur atoms, and not more than 2 atoms of sulfur in each chain, and provided further that the total number of carbon, oxygen, and sulfur atoms in each radical is from 3 to 40. Rz' and R2 of the formula represent monohydric alcohol residues which may each be (1) a satu- "ice rated straight chain aliphatic hydrocarbon radical contaimng not more than 5 carbon atoms, (2) a saturated branched chain-hydrocarbon radical containing 3 to 20 carbon atoms, or (3) a series of saturated aliphatic hydrocarbon radicals, straight chain or branched, interhnked by oxygen or sulfur atoms, or both oxygen-and sulfur atoms, the total number ofcarbon, oxygen, and sulfur atoms being from 4 to 20, and the number of oxygen or sulfur atoms or both in the radical being not more than 5. There should also be a chain of at least 2 carbon atoms between the acid radical and the first oxygen or sulfur atom and a similar chain of at least 2 carbon atoms between each pair of oxygen or sulfur atoms in the radical. Rs of the formula represents a glycol radical, and it may consist of a saturated aliphatic hydrocarbon group, straight chain or branched, containing 2 to 20 carbon atoms, or it may be a series of saturated aliphatic hydrocarbon radicals interlinked by oxygen or sulfur atoms, or by both oxygen and sulfur atoms, provided there are at least 2 carbon atoms between each carboxyl group and the nearest oxygen or sulfur atom and at least 2 carbon atoms between each pair of oxygen or sulfur atoms in the chain. The total number of carbon, oxygen, and sulfur atoms in the entire Ra radical is from 5 to and the number of sulfur atoms is not greater than 2. To provide a .product having suificient viscosity for lubricating purposes the molecular weight of the entire ester should be at least 300, and to provide a product having a pour point sulficiently low, i. e., an A. S. T. M. pour.point not higher than -10 F., it is generally necessarythat the molecule contain at least 2 atoms of oxygen or sulfur, or both oxygen and sulfur, in ether or thioether linkages.

Among the various components of the complex esters of the present invention certain preferences may be pointed out as giving the optimum of desired properties from the standpoint of serviceas a lubricant. The preferred dibasic acids are the straight chain dibasic acids of the paraffinic group having from 6 to 10 carbon atoms per molecule. The preferred glycols are the polyethylene glycols of the formula HO (CHaCHaO nCHZCHZOH where n is 1 to 26.

Illustrative examples of the dibasic acids which may be employed 1n the synthesis of the complex esters of the present invention are the following:

Oxalic acid Malonic acid Succinic acid Glutaric acid Adipic acid Pimelic acid Suberic acid Azelaic acid Sebacic acid Brassylic acid Pentadecanedicarboxylic acid Tetracosanedicarboxylic acid Cs-Cza alkenylsuccinic acids Diglycolic acid Thiodiglycolic acid The 04-024 alkenyl succinic acids listed above are prepared by condensing olefins or mixtures of olefins with maleic anhydride.

The monohydric alcohols employed are typified by the following:

Methyl alcohol Ethyl alcohol n-Butyl alcohol 2-ethylhexyl alcohol Ethylene glycol mono-n-butyl ether Ethylene glycol mono-2-ethylbutyl ether Ethylene glycol mono-2-ethylhexyl ether Ethylene glycol mono-terL-octyl' ether p-n-Butylmercaptoethanol fi-terL-Octylmercaptoethanol -n-Dodecylmercaptoethanol iethylene glycol mono-n-butyl ether 3 Diethylene glycol mono-2-ethylbutyl ether Diethylene glycol mono-Z-ethylhexyl ether Propylene glycol mono-butyl thioether I Propylene glycol mono-tert.-octyl thioether Propylene glycol mono-n-dodecyl thioether n-Butylmercaptoethoxyethanol tert.-ctylmercaptoethoxyethanol n-Dodecylmercaptoethoxyethanol n-Butylmercaptopropoxypropanol tert.-Octylmercaptopropoxypropanol n-Dodecylmercaptopropoxypropanol Propylene glycol mono-n-butyl ether Dipropylene glycol monomethyl ether Dipropylene glycol monoethyl ether Dipropylene glycol mono-n-butyl ether Tripropylene glycol monomethyl ether Tripropylene glycol monoethyl ether Tripropylene glycol mono-n-butyl ether Propylene glycol monoisopropyl ether Dipropylene glycol monoisopropyl ether Tripropylene glycol monoisopropyl ether Many of the above listed ether alcohols, formed by the reaction of ethylene oxide or propylene oxide with aliphatic alcohols, are known in the industry as Dowanols, Carbitols, or Cellosolves."

A group of alcohols especially adapted for use in the present invention are the so-called 0x0 alcohols, prepared by the reaction of carbon monoxide and hydrogen upon the olefins obtainable from petroleum products. Materials such as diisobutylene and C1 olefins are suitable for this purpose, also higher weight olefinic materials are sometimes employed. The alcohols obtained in this manner normally have a branched chain structure. The 0x0 process for the preparation of alcohols was developed in Germany and first described 1n this country in Roelen U. S. Patent No. 2,327,066, granted August 17, 1943.

The glycols employed in preparing the esters of the present invention include ethylene glycol and any of the paraffinic homologues of the same contamlng up to 20 carbon atoms.. These homologues may include, for example, propylene glycol, butylene glycols, pmacone, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, and the like. Since the glycols may also contain oxygen or sulfur atoms, compounds such as diethylene glycol, triethylene glycol, the polyethylene glycols of the formula where n is l to 26,

4 and th pol general form a e ypmpyline k ywls of the where R or R is a methyl group andthe other is hydrogen, and where n 1s 1 to 20, may likewise be employed. Glycols containing sulfur atoms in thioether linkages may also be employed, and these include such compounds as thiodiglycol and 1,2-b1s(Z-hydroxyethyl-mercapto)ethane. There also may used glycols containing both oxygen and sulfur In similar linkages; such a compound is his- [2-(2-hydroxyethoxy)ethyl]sulfide.

I t Wlll be understood that when glycols are employed which contain no oxygen or sulfur in the chain, at least two such non-carbon atoms should be introduced into the molecule by means of the acid or monohydric alcohol employed in the esterification, since these non-carbon atoms are required for producing products of sufliciently low pour point, as stated above. If desired, various addition agents may be incorporated 1n the esters of the present invention for the purpose of improving their properties with respect to their usefulness as lubricants. For example, antioxidants, viscosity index improvers, thickeners, pour depressants, dyes, etc., may be added.

Data will be given below showing the properties of several examples of complex esters within the scope of the present invention, indicating the adaptability of these esters to lubricating service. All of ese esters were prepared by a general esterification method which may be described in detail as follows: In a 1-liter round bottom reaction flask, fitted with a reflux condenser and water trap, were placed 0.5 mol of dibasic acid, 0.5 mol of monohydric alcohol, 1.5 grams of p-toluene-sulfonic ac 1d monohydrate (catalyst), and ml. toluene. The m1xtu re was refluxed until no more water collected in the water trap. After cooling, 0.25 mol of a glycol was added and the refluxing process resumed until more water collected in the trap. The mixture was washed with three l00-ml. portions of saturated aqueous sodium carbonate solution and one l00-ml. portion of water. After drying with "Drierite (anhydrous calcium sulfate) the matenal was filtered and stripped at a pressure of about 12 mm. to a bath temperature of about 225 C.

The results of tests of various properties of esters prepared by the above general method are shown in the H0(CH:CI-I:O)CI-I:CI*I:OH table of data which follows;

m Kinematic Viscosity ASTM Components of Ester Point 48TH 810 In 100 r. 210 r. m 5 1%) ii gifii h l 390 38. 730 7 n- 11 co 0 Trimethylenc glycol m o m 162 10 ls gifii 'rs 405 58.170 1 n- 11 co 0 0, 'Irlethylcne glycol 0 m 35 b d 2100111 as 30.400

xo 0 7.272 Trlethylena glycol 0 619 151 35 :1 h l 435 46.039 8.728

xo oo o Tlatmethylene glycol.-.--. 0 m 35 fifi l acid] 1 th 1 1th 386 25.010 I yeneg comonoe ye or 6.338 Thlodlglycol 0 M2 156 35 hi i 1 1 iso 1 th 435 so ass prop one g yco mono prop e or 11. 116 0. Tetraethylcne glycol. y m 141 36 ng ififi 455 48.943 see :0 co 0 8. 0. Thtmethylene glycoL- 602 35 0 ac 2-Ethylhemnol i 470 06. 758 12. 327 Tetmethylene glycol 0 M9 35 5 m ill??? 480 mass 12. 10

l x0 00 o 3 64 Tctmethyleno glycol 0 7 35 3 gi fi'i i 455 4a 800 :0 co 0 9. 541 Trlethylene gl col 0 574 162 10 (B -O" alkeny IllOtllItlO Mid Math 1 alcohol 486 245. 3 Z). 650 0. 648 106 -10 Trlet ylene glycoL- 8 i? in fi'i 420 37 x0 00 0-.-.-- .240 6. 'lctmethylene glycol.-- 407 o 688 35 il iiifi t i ass 24. 71 n- 11 co 0 0 5.287 0. Trimethylene glycol 35 Prepared by condensing a 0 -0 olefin mixture with maleic nnhydride.

The above data indicate that the esters constituting the subject matter of the present invention possess c eristics, particularly with regard to viscosity index and pour point, which indicate their suitability for general use as lubricating oils and particularly for use where the utilizatron of additives is not desirable. The esters of the present invention may also be blended with mineral lubricating oils to give lubricants of improved viscosity index and pour point.

What is claimed is:

1. As a new composition of matter, a compound of the formula R:OOCR1COORsOOCR1'COORa' wherein R1 and R1 are straight chain aliphatic hydrocarbon groups each containing from 0 to 8 carbon atoms, wherein R2 and R2 are branched chain aliphatic hydrocarbon groups containing from 4 to 20 carbon atoms each, at least one of said groups containing at least one atom of the group of oxygen and sulfur in ether linkage, and wherein Rs is a radical of the formula 5. As a new composition of matter, a compound of the formula wherein R1 is a branched chain aliphatic hydrocarbon radical of from 4 to 13 carbon atoms, wherein at is a number of from 7 to 8, and wherein n is a number of from 3 to 8.

6. A compound according to claim 5 wherein R: contains about 8 carbon atoms.

7. A compound according to claim 5 wherein x is about 8.

8. A compound according to claim 5 wherein n, is about 4.

9. As a new composition of matter, a compound of the formula CsH1'1OOC(CHa)sCOO(CHaCI-I:O)sOC I (CI-1:)aCOOH11Ca References Cited in the file of this patent UNITED STATES PATENTS 2,023,485 Malm Dec. 10, 1935 2,075,107 Frazier Mar. 30, 1937 2,295,165 De Groote Sept. 8, 1942 2,363,045 De Groote Nov. 21, 1944 2,375,529 De Groote May 8, 1945 2,379,251 Muskat June 26, 1945 2,392,621 Strain Ian. 8, 1946 2,415,366 Muskat Feb. 4, 1947 2,628,974 Sanderson Feb. 17, 1953 2,668,848 Neuworth Feb. 9, 1954 

1. AS A NEW COMPOSITION OF MATTER, A COMPOUND OF THE FORMULA 